1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a circuit for converting an internal voltage in a semiconductor device.
2. Description of the Related Art
In a semiconductor device, one method for converting an internal voltage comprises dropping an external power supply voltage to reduce power consumption. This facilitates applying an increased internal voltage to a circuit element such as a transistor during, e.g., a testing mode. As integration has increased, circuit size is reduced thus requiring smaller voltages for the smaller circuit components. However, because a manufacturer cannot freely lower an external power supply, it is necessary to generate an internal power supply voltage to provide the required lower voltage. FIGS. 1 and 2 illustrate conventional internal voltage conversion circuits in a semiconductor device.
In FIG. 1, a comparator 110 compares a predetermined reference voltage VREF with a feedback voltage and applies a compared result to a gate of a pull-up transistor 120. The drain of the pull-up transistor 120 comprises an internal power supply terminal which supplies an internal power supply voltage VINT. The voltage on the internal power supply terminal is divided by resistors R1 and R2 and fed back to an input port of the comparator 110. Here, the size of the feedback voltage applied to the comparator 10 is calculated in the following equation 1. ##EQU1##
In the internal voltage conversion circuit shown in FIG. 2, a comparator 130 compares a reference voltage VREF with a feedback voltage. A pull-up transistor 140 is switched according to the output of the comparator 130. Accordingly, the comparator 130, compares the reference voltage VREF with a feedback voltage, V .sub.feedback in equation 2, which is a function of V1, the voltage at the drain of transistor 140. The voltage V 1 is driven by a driving portion comprised of a comparator 150 and a pull-up transistor 160. The output of the circuit of FIG. 2 is an internal power supply voltage VINT. ##EQU2##
However, the foregoing conventional internal voltage circuits for a semiconductor device always provides a power supply voltage of a constant level internally. In particular, after packaging the memory in a plastic package, the level of the internal supply power supply is impossible to control. Therefore, semiconductor products undergo only a function test to detect various product inferiorities, which limits the type of screening for defects in the memories. These products could be more fully tested if the internal supply could be varied after the products are packaged.